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Fructose – The sweet nectar of body fat?


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As a result of fructose becoming such a media hot topic (and the result of this being lots of sound bites with little sensible information), we here at Precision Nutrition decided to set the record straight. So here’s our take on this hotly contested carbohydrate.

“Juice makes you fat!”

“High fructose corn syrup causes diabetes.”

“You shouldn’t eat fruit, it increases body fat!”

You’ve probably heard these battle cries before. And love them or hate them, they all have to do with the much maligned carbohydrate – fructose. As a result of fructose becoming such a media hot topic (and the result of this being lots of sound bites with little sensible information), we here at Precision Nutrition decided to set the record straight. So here’s our take on this hotly contested carbohydrate.

Juice boxes and cavemen

The general public typically associates fructose with fruit. And while that’s an accurate association since fructose makes up a portion of the carbohydrate in fruit, most of our daily fructose consumption comes from non-fruit sources.

Indeed, a majority of our fructose intake is not from fresh fruit, but from high fructose corn syrup and sucrose – both of which are found in soft drinks, processed foods, sweets, and in damn near everything in a bag, box, or plastic container. And not only are we getting fructose from high fructose corn syrup or fructose in general, we’re also getting it when we ingest sucrose since sucrose (or, table sugar) is a disaccharide made up of glucose + fructose.

500 years ago, the sugar industry was non-existent, and so was fructose in our diets. Fructose consumption was limited to a handful of items like honey, dates, raisins, molasses, and figs, which are all considered “dense” sources. Additional intake of fructose was from grapes, apples, persimmons, and berries. Of course, vegetables and protein foods have limited amounts of fructose and don’t contribute substantially to overall intake.

So, in the end, as you might have gathered, our human ancestors had little early dietary exposure to fructose…

…then, the sugar industry came to town.

A sugar factory in action

Sugar factories found cheap ways to extract – en masse – pure sucrose from sugar cane and high fructose corn syrup from corn. Interestingly, high fructose corn syrup has become a preferred source of sweetness and texture in the food manufacturing industry for primarily economic reasons.

You see, the American price for cane sugar is artificially high compared to the global price of corn. (This is due to governmental subsidies for corn and overproduction of corn for livestock). Therefore, since corn is cheaper than cane sugar, high fructose corn syrup is cheaper to produce than sugar. Picking up on the economic advantages of this shift, major soft drink manufacturers switched to HFCS as their primary sweetener in 1984. And they haven’t looked back since.

Fructose by the pound

As the consumption of HFCS has risen, so has the epidemic of obesity. This has led many to believe there is an association between the two. Indeed, food intake surveys have indicated that the average person consumes about 79 grams of added sugars each day (~316 calories or 15% of caloric intake), half of these 79g being in the form of fructose.

Whether or not this high consumption of fructose causes obesity or is just another symptom of poor eating and less activity in general (which, in turn, leads to obesity) is debatable. Indeed, food lobbyists have argued this point, effectively buffering themselves from government regulations that could cost the HFCS industry billions of dollars. However, what’s not debatable is this – the rise in HFCS consumption isn’t exactly helping the issue and, in our opinions here at PN, that’s the most important point.

How does fructose differ from glucose?

Since we’re talking sugars, let’s highlight the differences between fructose and glucose (the sugar that most of our ingested dietary carbohydrates become when they hit the bloodstream) here.

  • Fructose is absorbed through the intestine via different mechanisms than glucose.
  • In addition, fructose has a slower rate of uptake
  • Unlike glucose, fructose does not stimulate a substantial insulin release.
  • Fructose is transported into cells via a different transporter than glucose.
  • Once fructose is in the liver, it can provide glycerol, the backbone of triglycerides (fat), and increase fat formation.
  • Some people may have an inability to completely absorb fructose when given in a high dose of around 50 grams. (Note, that’s a lotta fructose. We’re talking 4-5 medium apples. Conversely, a 16 oz juice with HFCS can provide around 45 grams of fructose. Hello flatulence.)
  • Consuming glucose with fructose at the same time accelerates the absorption of fructose. This is one of the reasons that many sports drinks contain a mixture of sugars.

So, as you can see, there are some clear differences in absorption, digestion, and metabolism between fructose and glucose. Let’s go a bit deeper into this.

The liver is the major site of fructose metabolism. In the liver, fructose can be converted to glucose derivatives and stored as liver glycogen – which is good if you’re physically active.

However, the liver’s ability to do this is limited – which isn’t so good. Indeed, with very high single-serving doses of fructose, the fructose that arrives at the liver can easily be converted to fat. And this is very much more prominent in clients with high blood lipids, insulin resistance, or Type 2 diabetes.

Now, blood levels of fructose are not directly subject to tight hormonal regulation. And this is one of the reasons fructose has a low glycemic response – which is often considered a positive.

However, again on the negative side, while high intakes of fructose can lead to the synthesis of fat, it also fails to stimulate the production of leptin.

Since leptin is a hormone involved in the long-term regulation of energy balance, the decrease in leptin production associated with chronic high fructose intake can have harmful effects on the regulation of energy intake and body fat.

In other words, with HFCS, you never get those “I’m full” signals from the brain. So you keep eating.

So, although fructose is low on the glycemic scale and can help replenish liver glycogen in the very physically active, excess intakes of fructose can lead to the new creation of fats in the liver as well as a short circuiting of our energy balance and body fat regulating systems.

As a result, central obesity, low levels of good cholesterol, high levels of bad cholesterol, high triglycerides, and poor appetite control have been linked to consuming high amounts of high fructose sweeteners.

Fructose malabsorption

Another problem associated with fructose consumption is fructose malabsorption. Like lactose intolerance, gluten allergy, and other food-related GI problems, it’s classified as a digestive disorder. Fructose malabsorption occurs when fructose carriers in the intestinal cells are lacking. The result is that high amounts of fructose remain in the intestine and cause bloating, flatulence, and diarrhea.

How big of a problem is this? Well, fructose malabsorption occurs in nearly 30-40% of North America and Europe, with only half exhibiting regular symptoms.

What to do about fructose

After reading even just this brief fructose review, many people will likely have misgivings when it comes to fructose. And for good reason.

However, it’s important not to make the mistake of thinking that the small amounts of fructose in fruit will be problematic. Remember, all the problems happen at very high intakes of fructose when liver glycogen is likely to be maxed out.

Indeed, it’s highly unlikely that consuming whole, unprocessed, fresh fruits will promote energy imbalances and body fat gains? However, it’s very likely that regular consumption of fructose rich fruit juices and foods will cause these problems.

So, when should you eat your fruits? Well, the optimal times to consume fruit – if you don’t have any absorption issues – may be first thing in the morning, before workouts and/or after workouts.

In the end, top researchers have concluded:
The intake of naturally occurring fructose from an unprocessed, whole food diet is low and unlikely to contribute to any negative metabolic consequences.

And as we always like to remind people: whole fruits are rarely (if ever) the cause of major body fat problems. We don’t know many people who go on “pear benders” or “blueberry binges.”

Note: This article was first published at www.t-nation.com

References

Click here to view the information sources referenced in this article.


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